1. Field of the Invention
The present invention relates to an apparatus and method for measuring amounts of overlap of sheet-shaped members constituting a tire.
2. Description of the Related Art
Conventionally, a green tire is formed by winding sheet-shaped members, such as an inner liner, a carcass ply, belts, and a tread, having been molded into predetermined lengths of sheets, sequentially around a tire molding drum and attaching annularly formed beads to the carcass ply. Each of these sheet-shaped members is molded in advance into a predetermined length relative to the drum circumference dimension to create a predetermined amount of overlap between the winding start end and the winding completion end when it is wound around the molding drum. However, these sheet-shaped members, which are each made up of uncured rubber material, can get deformed with extension or shrinkage from the predetermined molding dimensions during conveyance or winding around the molding drum. Thus, there may be cases of excess or insufficient amount of overlap when the sheet-shaped members are actually wound around the molding drum.
The setting of the amount of overlap varies with the lap joint which retains the overlap state even after the subsequent process of curing and the butt joint which has a butted state of sheet after curing. Especially when the butt joint is employed, the amount of overlap at the time of molding needs to be accurate, and therefore the measurement of the amount of overlap is carried out to ensure that there is actually the predetermined amount of overlap after the sheet-shaped member is wound around the molding drum.
For example, the amount of overlap is measured using a plurality of two-dimensional laser sensors and an encoder for detecting the rotation of the molding drum. The plurality of laser sensors are set such that the light track of the cast laser light is slanted with respect to the width direction on the molding drum surface. And the plurality of laser sensors are arranged at a predetermined distance apart from each other so that the laser light cast from the respective laser sensors covers the whole width of the molding drum.
Firstly, a sheet-shaped member is wound around the molding drum with the laser light cast from the laser sensors, and the position of the winding start end crossing the light track of laser light is detected as the molding drum is rotated. At the same time, the distance of movement of the detected winding start end is detected by the encoder. Next, the length of the sheet-shaped member wound around the molding drum is measured by detecting the position of winding completion end crossing the light track of laser light as the molding drum is rotated. Now the amount of overlap is measured by determining the difference between the measured length of the sheet-shaped member and the circumference length of the molding drum.